On an MRI device, a subject (usually a human body) is inserted into a uniform static magnetic field generated by a static magnetic field coil (such as a superconductive coil) in an inner image capturing space. The MRI device irradiates the human body with RF pulses generated by an RF coil for exciting nuclear spins; thereby receives magnetic resonance signals generated from an inside of the body of the subject; and thus obtains a topographic image for medical diagnosis. Herein, a gradient magnetic field coil device generates a gradient magnetic field (with a primary gradient), which is temporally pulsed and spatially gradient, and makes addition of three-dimensional position information in the subject laid in the image capturing space.
In recent years, in order to obtain a high image quality of the above-described topographic image and shorten the image capturing time, a high gradient magnetic field intensity and high speed driving are required of a gradient magnetic field coil device. Improvement of the performance of the power source for a gradient magnetic field, and the like, has made it possible to realize these requirements by applying a large intensity current to the gradient magnetic field coil device and switching at a high speed. Accompanying this realization, when a pulsed gradient magnetic field is generated, eddy currents flowing in conductors such as a gradient magnetic field coil device also become high, and heat generation by the eddy currents and the magnetic field generated by the eddy currents (eddy current magnetic field) become significant. As an eddy current magnetic field distorts the gradient magnetic field in an image capturing space, the image quality of the above-described topographic image may be deteriorated. Particularly, components of even orders higher than or equal to the secondary order of an eddy current magnetic field need to be made low because they cannot be compensated by a correction pulse, which is of a primary component, for correcting the gradient magnetic field. In this situation, it is offered to dispose a conductive ring so that the even order components substantially become zero by an eddy current magnetic field (for example, refer to Patent Document 1). Further, in order to reduce heat generation by eddy currents, it is also offered to decrease the width of a coil conductor in a region where the interlinked gradient magnetic field is intensive (for example, Patent Document 2 and the like).